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Biomedical subjects

B W McDonald

Publications and source records attributed to B W McDonald.

14 recordsLinked to original sources
PubMed1994

Two random effects models for multivariate binary data.

We consider two regression models for multivariate binary data in the case that the marginal success probabilities are unequal. The first model is based on an additive random effect operating on the probability scale. The second model assumes a discrete random effect operates on the logit scale. Consequently the interpretation of the regression parameters differs for the two models. Their use is illustrated by application to some dental data.

Biometry↗
PubMed1990

The prevalence of overhanging margins in posterior amalgam restorations and periodontal consequences.

The purpose of this study was to determine the prevalence of overhanging margins and associated periodontal status in 100 patients who had received completed treatment by final year dental students. Pockets, bleeding on probing and clinically detectable overhanging margins were recorded on all posterior teeth. Overhanging margins on approximal restorations were detected by use of bitewing radiographs. 1319 teeth were examined in which 2117 restored surfaces were evaluated. Of these, 1186 (56%) had overhanging margins. 62% of all approximal restorations had overhanging margins while 35% of buccal and 40% of lingual restorations had overhanging margins. 59% of new approximal restorations placed in previously unrestored surfaces had overhanging margins, and 595 overhanging margins identified on pre-treatment radiographs were still present on post-treatment radiographs. 64.3% of pockets adjacent to overhanging margins were greater than 3 mm, compared with 23.1% of pockets adjacent to unrestored surfaces and 49.2% of pockets adjacent to restorations without overhanging margins. A similar association existed between restorative status and bleeding. 32% of pockets adjacent to overhanging margins bled on probing compared with 10.5% of pockets adjacent to unrestored surfaces and 21.6% of pockets adjacent to restorations without overhanging margins. Periodontal disease was more severe when overhangs were present. However, when approximal overhanging margins were adjacent to an edentulous space, the periodontal effects were lessened. When adjacent to neighbouring teeth, overhanging margins also significantly affected the periodontal status of those teeth.

Adult↗
PubMed1990

Concepts determining statistical analysis of dental data.

This paper reviews some approaches to statistical analysis of dental data. Often dental data consist of more than one observation per patient which may not be independent, and consequently some standard statistical methods based on independence of all observations are inappropriate. This paper seeks to make the dental researcher and the consulting statistician aware of some of the efficient approaches that can be used to analyse the data successfully. No specialist statistical knowledge is assumed. Rather the goal is to increase awareness of what can be done. The statistical layman is introduced to some basic concepts, while references are given for the mathematically-minded reader. The data of Pack, Coxhead and McDonald is used as a springboard for this discussion.

Data Interpretation, Statistical↗
PubMed1987

Urine glycosaminoglycans in a reference population: effects of age, body surface area, and postmenopausal status.

Urine glycosaminoglycans and hydroxyproline have been measured in an adult reference population containing significant numbers of those over 65 years. Urine concentrations of glycosaminoglycans remain constant into old age providing body weight is maintained and correlate significantly with body surface area. The urine ratio of glycosaminoglycans to creatinine rises markedly in women after menopause resulting in a bimodal frequency distribution. This ratio is worth further investigation as a marker of postmenopausal osteoporosis.

Adult↗
PubMed1986

Multivariate analysis of the long-term results of coronary artery bypass grafting performed during 1976 and 1977.

The results of 492 consecutive coronary artery bypass grafting operations performed for angina in the 2-year period from 1976 to 1977 were evaluated 77 months after surgery. Follow-up was complete in 99%. In 80% of patients angina severity was New York Heart Association functional classes III or IV. An ejection fraction of less than 50% and left ventricular end-diastolic pressure of more than 15 mm Hg were each present in one-third of patients. Thirteen patients (2.6%) died in hospital and 70 (14%) died later during the follow-up period. Twenty-six reoperations were performed for recurrent angina (5.3%). Angina was initially relieved by operation in 97% of patients, but only 57% were alive and free of angina 6 years after their operation. Despite this, 91% of patients at last follow-up were in functional class I or II and 94% thought their symptoms were better than preoperatively. The mean postoperative time of onset of angina, estimated independently by family physicians and patients, was 33 months. The significant preoperative predictors of late death were a low left ventricular ejection fraction, previous myocardial infarction, prior cardiac surgery, increased cardiothoracic ratio and the number of coronary arteries with significant narrowing.

Adult↗
PubMed1986

Is there seasonal variation in the prescribing of antidepressants in the community?

The prescribing of antidepressants by general practitioners might be expected to reflect the incidence of depression in the community. In a two-year study of the prescriptions issued by English general practitioners to a population of 40,000 people, the rates of initiating treatment with antidepressants were analysed by month. There was seasonal variation in new antidepressant prescribing for men (p less than 0.025), with peaks in early June and early December, but no significant seasonality for women. The bimodal pattern in men was similar to a recently reported seasonal variation in general practice consultations for depression.

Antidepressive Agents↗
PubMed1984

Regional circulatory responses to 96 hours of hypoxia in conscious sheep.

Exposure of adult ewes to normobaric hypoxia (PaO2 40 mm Hg) for 96 h led to increases of VE (+ 54%), while VO2 decreased by 48%. PaCO2 declined progressively to stabilize at 24 (+/- 1.5 SE) mm Hg by 24-48 h. Cardiac output (thermodilution) was elevated temporarily for 24 h (23-34%) but then returned to normoxic levels, while heart rate (28-42%) and pulmonary artery pressure (38-56%) were increased for the duration of hypoxia. Cerebral blood flow (radiolabelled microspheres) increased transiently for 48 h from 65.9 (+/- 4.4) to 100.4 (+/- 9.9) ml X min-1 X 100 g-1 with no change in its regional distribution. Coronary flow was elevated for the duration of hypoxia from 181 (+/- 15) to between 280 (+/- 33) and 350 (+/- 37) ml X min-1 X 100 g-1 with a more pronounced increment in right heart flow, and a decline in the endocardial/epicardial flow ratio. These regional flow increases resulted from a sustained decrease in pancreatic flow from 234 (+/- 11) to 125 (+/- 13) ml X min-1 X 100 g-1 for 96 h, with persisting decreases in splenic flow from 249 (+/- 30) to 100 (+/- 18), and in renal cortical flow from 787 (+/- 70) to 540 (+/- 31) ml X min-1 X 100 g-1, occurring at 48 and 72 h, respectively. Therefore, there is a redistribution of cardiac output during 96 hours of hypoxia with increased flows to heart and brain, and decreased flows to abdominal viscera.

Animals↗
PubMed1984

Metabolism of vitamin B-6 by human liver.

The enzymes that metabolize vitamin B-6 were analyzed in liver biopsy samples from five patients without hepatic disease by using methods optimized for small samples. Pyridoxal kinase (EC 2.7.1.35) activities were 11.2 +/- 3.6 nmol/minute per gram of tissue and 0.16 +/- 0.05 nmol/minute per milligram of soluble protein (mean +/- SD); a clear dependence of the activity on zinc as the divalent cation was observed. Pyridoxine (pyridoxamine) 5'-phosphate oxidase (EC 1.4.3.5) activities, when using N-(5'-phosphopyridoxyl)-[3H]tryptamine as the substrate, were 0.64 +/- 0.22 pmol/minute per milligram of protein and 47 +/- 19 pmol/minute per gram of tissue. The activities were 63 +/- 18% lower when riboflavin 5'-phosphate was omitted from the assay; hence, it appears the oxidase is only partially saturated with its cofactor. The pyridoxal 5'-phosphate hydrolase(s) activities at alkaline pH were 282 +/- 183 nmol/minute per gram of tissue and 4.0 +/- 3.2 nmol/minute per milligram of particulate protein. Pyridoxal was rapidly oxidized to pyridoxic acid (28.1 +/- 19.8 nmol/minute per gram of tissue and 0.37 +/- 0.24 nmol/minute per milligram of soluble protein) by soluble enzyme(s), and the rate was unaffected by pyridine nucleotides. These experiments constitute the first quantitative analyses of the enzymes responsible for metabolizing vitamin B-6 in human liver, and provide data for interpreting the pharmacokinetics of B-6 utilization by humans, as well as methods for investigating diseases with aberrant metabolism of this nutrient.

Alcohol Oxidoreductases↗
PubMed1984

Cardiovascular and renal responses to head-out water immersion in canine model.

Water immersion (WI) of anesthetized dogs to the midcervical level in the vertical sitting position under thermoneutral conditions (38 degrees C) leads to generalized increases in regional blood flows (radiolabeled microspheres) to most tissues. The increased flows can be accounted for by increased local VO2 in some tissues (heart, respiratory muscle), or by local heating (skin, fat). However, an alteration in the relation between cardiac output (Q) and VO2 appears to play a role in the large flow increments observed in skeletal muscle and abdominal viscera in WT. Studies of conscious, chronically instrumented dogs during 100 min of thermoneutral WI at 37 degrees C in the quadruped position indicate that both left atrial and aortic transmural distending pressures and left ventricular contractile performance (LV dP/dtmax) increase, while total peripheral resistance is unchanged. Cardiac output increases largely in association with an increase of heart rate. In addition, urine flow, sodium excretion, and osmolal clearance all increased. The cardiovascular adjustments occurred more rapidly than the renal responses. These results indicate that the conscious dog may be useful for investigation of physiological mechanisms involved in the WI response.

Abdomen↗
PubMed1982

Regional circulatory responses to head-out water immersion in anesthetized dog.

Thermoneutral head-out water immersion (WI) of humans leads to a sustained elevation of cardiac output (QCO), while systemic VO2 is unchanged. However, the regional blood flow responses (Qr) to WI are largely unknown. In eight dogs anesthetized with pentobarbital sodium, relative to the control vertical position in air with the chest and abdomen upright (Erect1), after 30 min of WI at 38 degrees C the QCO (thermodilution), stroke volume, and aortic pressure were elevated (P less than 0.01) by 88.5 +/- 6.4% (SE), 55 +/- 9%, and 29 +/- 4% from levels of 2.24 +/- 0.01 1 X min-1, 18.4 ml +/- 1.7, and 109 +/- 7.9 mmHg, respectively. Qr (ml X min-1 X 100 g-1), measured by 15 microns-radiolabeled microspheres at WI30 min relative to the Erect1 levels, increased (P less than 0.01) in the stomach (104 +/- 27%), jejunum (78 +/- 19%), ileum (102 +/- 23%), liver (hepatic artery) (485 +/- 46%), pancreas (200 +/- 44%), spleen (88.7 +/- 33%), renal cortex (88 +/- 30%), left ventricle (157 +/- 15%), skin (726 +/- 30%), fat (680 +/- 43%), gastrocnemius (200 +/- 36%), triceps (414 +/- 61%), intercostals (317 +/- 44%), and diaphragm (477 +/- 24%). Qr responses at WI10 min were largely similar. Rectal temperature and VO2 were unchanged during WI. In the lateral recumbent position in air, QCO rose by 44.3% (P less than 0.01), but only hepatic arterial Q rose significantly (89 +/- 29%). Therefore, there may be a partial uncoupling of the normal Q/VO2 relationship in WI.

Abdomen↗
PubMed1981

Control of ventilation during graded exercise in the dog.

We analyzed the time courses of the VE, VT, and f responses to graded levels of exercise produced by increases in treadmill speed at preset inclines in 207 experiments on 15 tracheostomized dogs. At the onset of work, VE increased within 1-2 respiratory cycles (VE fast), and then either remained constant, or decreased. Following this time delay (TD), VE rose more slowly (VE slow) to attain a stable plateau (Dejours). The amplitude of VE fast, VT, and f during the TD were independent of the work load. However, the duration of the TD and the amplitude of the component mediating VE slow were workload dependent. The VE fast and the VE during the TD are the major components of the total VE response at low work levels (VO2 = 30-40 ml . min-1 . kg-1) and are mediated primarily by increased f, whereas, at higher VO2 (70-90 ml . min-1 . kg-1), VE slow is mediated largely by increased VT and this component is engaged earlier to make a greater contribution to the total VE response. In the conscious dog, the total VE response to exercise appears to be comprised of both neural and humoral components when thermal stress is minimal.

Animals↗
PubMed1980

Influence of CO2 on cardiovascular response to hypoxia in conscious dogs.

The modulating effect of CO2 on the circulatory response to hypoxia in chronically instrumented conscious dogs was examined over a wide range of arterial partial pressure of O2 [PaO2 (from 80 to 25 Torr)] during a 41-min rebreathing period at three CO2 levels: hypocapnia (from PaCO2 of 32 to 18 Torr), eucapnia (32 Torr), and mild hypercapnia (40 Torr). Eucapnic and hypercapnic hypoxic responses were also measured after sinoaortic denervation (SAD) to assess the arterial chemoreceptor and baroreceptor reflex contributions. Elevating PaCO2 attenuated the tachycardia during hypoxia and produced progressively greater systemic, renal, and splanchnic vasoconstriction before but not after SAD. Vagal block converted the rises in renal and splanchnic flows observed during hypocapnic hypoxia to declines. The increase in left ventricular dP/dtmax was not affected by varying PaCO2 either before or after SAD. Coronary flow increased an additional onefold during hypoxia when PaCO2 was elevated both before and after SAD, but the tension-time indices did not differ significantly. These results indicate that: a) cardiopulmonary vagal afferents effectively counteract chemoreflex-induced vasoconstriction during hypocapnic hypoxia; b) chemoreflex vasoconstriction predominates in the renal and splanchnic beds when PaCO2 is elevated; c) the sinoaortic reflexes restrain the heart rate, but not the contractility response to hypoxia when PaCO2 is increased; and d) the augmented coronary vasodilation produced by CO2 is probably mediated by local CO2-hypoxic interactions.

Animals↗